1. Field of the Invention
Aspects of the present invention relate to a two-component developing unit, and more particularly, to a two-component developing unit improving a delivery screw used in returning a toner.
2. Description of the Related Art
Conventionally, an image forming device includes a feeder, a developing unit, a fixing unit, and a discharge unit. The feeder supplies a printing paper into the image forming unit. The developing unit selectively coats a developer on the printing paper and forms a predetermined image. The fixing unit fixes the coated developer on the printing paper. The discharge unit receives the printing paper fixed with the developer from the fixing unit and discharges the received paper outside of the device.
The developing unit comprises an opto photo-organic conductor (OPC), a developing roller, and transferring roller. A latent image is formed on the OPC, which is exposed to a predetermined light. The developing roller supplies the developer to the latent image and develops the image. The transferring roller transfers a developed image formed on the OPC to the printing paper.
The developing unit can be of two types. One type is a one component developing unit, which uses only the toner. Another type is a two-component developing unit, which uses the toner and a carrier. The two-component developing unit has been widely used because this type can develop at high speed as compared with the one component developing unit. Further, the two component developing unit has good reproducibility in gradation.
The conventional two-component developing unit includes a carrier circulating part, which mixes the toner with the carrier and circulates the carrier to deliver to the developing roller. Where the toner is supplied to a circulating pathway in which the carrier circulates, the developing roller may receive the toner which is not sufficiently mixed or charged. Therefore, a toner supply part, which supplies the toner, is mounted outside the carrier circulating pathway so that the toner is sufficiently charged in the delivering process.
In order to allow the toner to be mixed and delivered with the carrier in where deliverability of the toner has otherwise decreased when the toner supply part supplies the toner to outside the carrier circulating pathway, a two-way delivery needs to deliver the toner to inside the carrier circulating part. That is, the carrier is delivered to near the toner supply part, at the same time, the toner and the carrier are delivered to near the carrier circulating part.
FIGS. 1 and 2 are schematic views illustrating a conventional two-component developing unit. As shown therein, the two-component developing unit 1 comprises an OPC 10, a developing roller 20, a carrier circulating part 30, a toner carrying part 40 and a toner supply part 50. The OPC 10 forms a latent image. The developing roller 20 is made of a magnetic material and receives the toner from the carrier circulating part 30. The developing roller 20 supplies the received toner to the latent image formed on the OPC 10, which then develops the image. The carrier circulating part 30 includes the carrier. The carrier circulating part 30 mixes the carrier with the toner, and circulates the carrier to deliver the toner to the developing roller 20 to form the pathway A-B-C-D-A. The toner supply part 50 is spaced from the carrier circulating part 30 and supplies the toner from outside of the carrier circulating pathway A-B-C-D-A.
The carrier circulating part 30 comprises a first delivering screw 32, a second delivering screw 34, a first sidewall 36 and a second sidewall 38. The toner and the carrier are mixed and delivered by the first delivering screw 32 in an “A” direction, and are redirected in the “B” direction at the first sidewall 36. The second delivering screw 34 delivers the mixed toner and carrier in the “C” direction. In this process, the carrier is carried to the developing roller 20 by a magnetic force generated by the magnetic material of the developing roller 20. At the same time, the toner attached to the carrier is supplied to the developing roller 20. The toner and the carrier, which are delivered by the second delivering screw 34, are redirected and moved in the “D” direction by the second sidewall 38 and are delivered to the first delivering screw 32.
The first delivering screw 32 close to the toner supply part 50 is formed to tilt downwardly in a predetermined angle d. A side of the first delivering screw 32 forms an upper stream, and a side of the second sidewall 38 and the toner carrying part 40 extended from the second sidewall 38 form a lower stream.
The toner carrying part 40 is disposed between the toner supply part 50 and the carrier circulating part 30. The toner carrying part 40 comprises a housing 41, a rotating shaft 42, and a longitudinal wing 43. The toner carrying part 40 is disposed at a lower side of a vertical direction of the carrier circulating part 30 so that the carrier flows from the carrier circulating part 30 to the toner carrying part 40 by its own weight. The rotating shaft 42 extends to the first delivering screw 32. The rotating shaft 42 near the toner supply part 50 is also formed to tilt downwardly in the predetermined angle d to correspond with a slope of the first delivering screw 32. The right delivering wing 44 is formed in a part of the rotating shaft 42 in an axial direction of the rotating shaft 42, and delivers the toner supplied from the toner supply part 50 and the carrier received from the carrier circulating part 30 to near the carrier circulating part 30 (“a” direction).
The longitudinal wing 43 is extended in a radial direction along the axial direction of the rotating shaft 42, and mixes the toner and the carrier. The longitudinal wing 43 decreases a delivering speed in the right direction (“a” direction) according to the right delivering wing 44 and ensures sufficient time for mixing the toner and the carrier. Further, the longitudinal wing 43 does not prevent the carrier from flowing into the toner carrying part 40 in a “b” direction along the slope.
The carrier flows into the toner carrying part 40 in the “b” direction by descending according its own weight along the slope of the carrier circulating part 30 and the toner carrying part 40. The right delivering wing 44 and the longitudinal wing 43 mix the carrier and the toner, and simultaneously deliver the mixed carrier and toner to the carrier circulating part 30 in the “a” direction. Accordingly, the conventional two-component developing unit 1 moves the carrier from the carrier circulating part 30 into the toner carrying part 40, at the same time, the two-component developing unit 1 mixes the toner, which is inputted newly, and the carrier, and then again supplies mixed toner and carrier to the carrier circulating part 30. Such a two-component developing unit 1 is disclosed in Japanese Patent First Publication No. 1995-253711.
However, the conventional two-component developing unit 1 uses a slope in order to move the carrier in the b direction. As such, the carrier circulating part 30 and the toner carrying part 40 are only able to deliver the carrier of the carrier circulating part 30 to the toner carrying part 40 to be mixed with additional toner using gravity. Therefore, where the two-component developing unit 1 does not maintain the predetermined angle d (such as when the developing unit 1 is placed on a sloping surface effectively reducing the predetermined angle d), the carrier can not flow back into the toner carrying part 40 in direction b. As such, the toner also can not be delivered to the carrier circulating part 30.
Further, the two-component developing unit 1 is a passive delivery system. Thus, the two-component developing unit 1 uses the carrier's own weight to deliver the carrier. Therefore, the two-component developing unit 1 is sensitive a variation of rpm (revolution per minute) of the first delivering screw 32 and the second delivering screw 34 and a variation of fluidity of the toner and the carrier. Since the fluidity of the toner and the carrier changes according to a particle diameter of the carrier and toner, the density (toner volume/carrier volume), a deterioration variation, a temperature, humidity, and a used frequency, the two-component developing unit 1 is not easy to ensure stably the toner delivery in view of its sensitivity to changes in foregoing various conditions.
Further, the longitudinal wing 43 of the two-component developing unit 1 mixes the toner and the carrier, but a delivering force, which can deliver the toner and the carrier in the “a” direction, is weak. Thus, the toner may be accumulated in the toner carrying part 40 and the toner may be delayed in being delivered to the carrier circulating part 30.